For local enhancement using mean and variance, the condition is:
The variance in the local window must be greater than zero to apply meaningful enhancement.
Explanation:
- Mean: The local mean calculates the average intensity of the pixels within a specified region or window around a target pixel.
- Variance: The local variance measures how spread out the pixel intensities are within the local neighborhood. High variance indicates more contrast or texture, while low variance indicates smooth or uniform regions.
Condition:
- Non-zero Variance: If the variance is zero (i.e., the region is completely uniform), no enhancement will be applied, as there's no contrast or feature to enhance. Therefore, for meaningful enhancement to occur, the local variance must be non-zero.
In summary, local enhancement is applied only when the variance is greater than zero, ensuring that the region has some level of detail or contrast to enhance.